- The definition of zealous is having passionate energy for a belief or purpose.
An example of zealous is a preacher in an energetic church.
Origin of zealousMedieval Latin zelosus ; from Ecclesiastical Late Latin zelus: see zeal
(comparative more zealous, superlative most zealous)
From Ancient Greek ζήλος (zēlos, “zeal, jealousy”), from ζηλόω (zēloō, “to emulate, to be jealous”).